Applications of capillary electrophoresis to the analysis of drug formulations and natural medicines

Capillary electrophoresis (CE) is a powerful method for drug analysis. However, even now, CE is still not used routinely as a quality control (QC) method. The present study focused on developing the CE method for practical use. First, the enantiomer separation of drugs by CE, employing various compounds as chiral selectors (CSs), was studied. In the case of 2,6-di-O-methyl-ss-cyclodextrin and sulfated cyclodextrins, the purity of the CS, i.e., degree of substitution (DS), strongly affected enantiorecognition of the drug. It was found that controlling the DS of these selectors is essential for practical use. In the case of carboxymethyl (CM) polysaccharides, the introduction of an ionic group (i.e., CM) enhanced the enantioselectivity, compared with the natural polysaccharides. 18-Crown-6 tetracarboxylic acid was useful for the enantioselectivity of amino acids (AAs). Employing chrysoidine as a chromophore additive, indirect enantiomer separation of free AAs was successful. Next, the developed CE methods were applied to actual formulation analysis. Purity testing, content uniformity and assays of the ingredients of commercial pharmaceutical formulations were successfully performed. Finally, micellar electrokinetic chromatography was applied for the identification and assay of marker substances of Chinese natural medicines. The results mentioned above demonstrated that the CE method can be used practically as a routine QC analysis.